Calculate usable capacity, fault tolerance, and minimum disk requirements for RAID 0, 1, 5, 6, and 10 configurations.
RAID (Redundant Array of Independent Disks) combines multiple physical drives into a single logical volume with varying levels of performance and fault tolerance. Choosing the right RAID level is one of the most impactful storage decisions an IT team makes. RAID 0 maximizes capacity and speed but offers zero protection—one dead disk means total data loss. RAID 1 mirrors drives for excellent redundancy but uses only half the raw capacity. RAID 5 and 6 use parity to balance capacity with fault tolerance, while RAID 10 combines mirroring and striping for top performance and redundancy.
This calculator instantly shows the usable capacity, fault tolerance (how many drives can fail), and minimum disk count for each RAID level. Enter the number and size of your drives, select a RAID level, and get clear results. It's essential for anyone building or planning a storage array—from home NAS setups to enterprise SAN deployments.
Understanding this metric in precise terms allows technology leaders to make evidence-based decisions about scaling, architecture, and infrastructure investment priorities for their organizations.
Choosing the wrong RAID level can waste expensive storage or leave you unprotected against drive failures. This calculator shows the trade-offs between capacity, performance, and fault tolerance for each RAID level, helping you make an informed decision. Having accurate metrics readily available streamlines incident postmortems, architecture reviews, and technology roadmap discussions with engineering leadership and product teams.
RAID 0: usable = disks × size; RAID 1: usable = size (mirror); RAID 5: usable = (disks − 1) × size; RAID 6: usable = (disks − 2) × size; RAID 10: usable = (disks / 2) × size
Result: 20 TB usable
With 6 disks of 4 TB each, RAID 5 uses one disk's worth for parity: (6 − 1) × 4 = 20 TB usable out of 24 TB raw. The array can tolerate exactly 1 disk failure. Storage efficiency is 83.3%.
RAID 0 delivers maximum capacity and sequential throughput but zero fault tolerance. RAID 1 provides perfect redundancy at 50% capacity efficiency. RAID 5 uses distributed parity for single-fault tolerance at good efficiency. RAID 6 adds a second parity disk for dual-fault tolerance—essential for large arrays. RAID 10 combines mirroring and striping for the best mix of performance and resilience.
Use RAID 1 for OS boot drives and small critical volumes. RAID 5 works well for read-heavy file servers with moderate capacity needs. RAID 6 is the standard for general-purpose storage with large drives. RAID 10 is the choice for databases and write-intensive applications where performance and redundancy both matter.
Modern solutions like ZFS RAIDZ, Ceph, and erasure coding offer more flexible alternatives with better scalability and efficiency than traditional hardware RAID. Consider these for new deployments, especially at scale.
RAID 5 or RAID 6 are common choices. RAID 5 offers good capacity efficiency with single-disk fault tolerance. RAID 6 is safer for large-drive arrays because it tolerates two simultaneous failures. For two-drive setups, RAID 1 (mirror) is the standard choice.
Traditional RAID uses the capacity of the smallest drive for all members. A 4 TB and an 8 TB drive in RAID 1 yields only 4 TB usable. Some modern NAS systems (SHR, Unraid) can use mixed sizes more efficiently.
Rebuild times depend on drive size and array activity. A 4 TB drive in a busy RAID 5 array can take 12–24 hours or more to rebuild. During this time, the array is vulnerable to a second failure, which is why RAID 6 is recommended for large drives.
RAID 10 mirrors pairs of drives, then stripes across the pairs. RAID 01 stripes first, then mirrors the stripes. RAID 10 is preferred because it can tolerate more specific failure combinations and rebuilds faster.
RAID 0 is suitable only for non-critical data where maximum speed and capacity are needed—such as video editing scratch disks or temporary render farms. Any single drive failure destroys all data in the array.
A hot spare is an unused drive that automatically replaces a failed drive, starting the rebuild process immediately. This reduces the vulnerability window from hours (waiting for a replacement) to minutes. Most enterprise arrays include at least one hot spare.